1. Field of the Invention
The present invention relates to a loosely coupled multiprocessor system and, more particularly, to a loosely coupled multiprocessor system for supervising the operating state of a plurality of processors by means of a supervisory ring.
2. Description of the Related Art
In general, a loosely coupled multiprocessor system comprises a plurality of processors and those processors are interconnected by a bus dedicated to inter-CPU data communications or a network such as a local area network (LAN). In such a loosely coupled multiprocessor system, each processor is operated by an individual operating system. For this reason, even if a processor becomes unable to operate normally due to a failure in its hardware or software, the failing processor may be replaced with another processor, thus maintaining the reliability of the entire operation of the loosely coupled multiprocessor system.
The failing processor can be discovered by a process of supervising whether or not the processors are operating normally. As supervisory processes, the following two methods are known.
One of the methods is for each of the normally operating processors to broadcast a message, indicating that it is operating normally, to all of the other processors. With this method, since the operating state of each processor is broadcast to all other processors, each processor can identify the operating states of the other processors, namely whether they are either in the normally operating state or in a failed state. With this method, however, the message of normal operation has to be continually issued, thus impairing the main purpose of the loosely coupled multiprocessor system, i.e. the data processing function, when a large number of processors are involved in the system.
The other supervisory method is to divide each of the processors composing the loosely coupled multiprocessor system into a master processor and a slave processor so that each of the master processors can supervise the operating state of its respective individual slave processor. With this method, messages for supervision will not be continually issued in the multiprocessor system as opposed to the former method. However, if a failure should occur in a master processor, the other processors will not be able to identify the occurrence of that failure and, moreover, the operating state of the slave processor of the failing master processor will not be supervised.